1. Field of the Invention
This invention relates to a battery control apparatus and management method of a battery, and particularly to such apparatus or method having function to check residual amount of battery power. For example, this invention is applicable to an electric bicycle, a personal computer, a portable telephone or the like, and the residual amount of battery power is detected based on both integrating current and terminal voltage of the battery.
2. Description of the Related Art
Many apparatus powered by a battery usually have a function to detect a residual amount of battery power left in the battery. Detection of the residual amount of battery power improves convenience of the battery-powered apparatus. As well known, a current integration method or a terminal voltage method is used for detection of the residual amount of battery power.
In the current integration :method, a full charge capacity or a residual capacity after the end of discharge is revised by a charge and discharge power of the battery obtained by integrating charge and discharge current. In this current integration method, detection precision of the residual amount of battery power is deteriorated, because detection error of charge and discharge current is accumulated by repetition of charging and discharging operation. Accordingly in order to improve detection precision, not only detection precision of a charge and discharge current is raised but also at a full charge or the end of discharge, the residual amount of detected battery power is reset by such as full charge capacities.
However, in the detection of the charge and discharge current, there is a problem that discharge current changes according to an operating condition of the connected various devices. Namely 1 [mA] degree of error may occur for a charge and discharge current of 10 [A] even if a charge and discharge current is measured by enough measurement precision.
In the current integration method, the residual amount of battery power detected by full charge capacities is reset at full charge or at the end of discharge, detection error of such charge and discharge current can be canceled. However, error is accumulated by the residual amount of detected battery power, and detection precision falls. if charging and discharging is repeated within a range that the battery does not reach to the end of discharge or a full charge. Even if a detection result that the power of the battery is still left is obtained in the current integration method, there is the case that the detected power actually can not be used for driving an apparatus. In this case where the current integration method is applied for detecting the residual amount of battery power, the battery suddenly goes down.
On the contrary, the voltage method detects the residual amount of battery power based on the relation between terminal voltage of the battery and the residual amount of battery lower (accumulated electricity amount). In other words when the battery discharges electricity with constant discharge current, the terminal voltage gradually goes down by about constant property as shown in FIG. 6. Accordingly the residual amount of battery power can be detected by measuring the terminal voltage of the battery.
Property of the relation between the terminal voltage and the residual amount of battery power ""shows the residual electricity amount based on the full charge power. The characteristics of relation between residual amount and terminal voltage of the battery shows charging capacity of residual amount based on the full charging power. Thereby if the ratio (accumulated electricity amount%) of the residual amount relative to full charging power is used, one characteristic curve can be applied to various kinds of batteries in spite of volume of full charging capacity. In case of this method, the operation processing using a full charge capacity value is necessary for detection of the residual amount of battery power.
In case of this method, accumulation of error does not occurs like as a case by the current integration, method. Furthermore, error becomes small as it becomes near the end of discharge in case of this voltage method. Accordingly sudden battery shortage as a case by the current integration method can be reduced.
By the way, the terminal voltage of the battery varies with internal resistance according to the charge:, and discharge current. Accordingly in the case of the voltage method, it is necessary to revise detected terminal voltage according to the charge and discharge current in order to apply to this characteristic curve. If the temperature is high, the internal resistance becomes low and if the temperature is low, the internal resistance becomes high. Namely, the internal resistance varies with temperature within a range of several times. Accordingly, in case of this voltage method, error in the detected residual amount of battery power becomes large only if charge and discharge current is large. In addition, if temperature is low, the error in the detected residual amount of battery power becomes large. Accordingly, in the voltage method, there is the problem that precision is not so good.
As a method of one solving this problem, the property between the terminal voltage and the residual amount of battery power is recorded at various charge and discharge current, and the residual amount of battery power is detected corresponding charge and discharge current. In case of this method, there is the problem that a construction becomes complicated in order to record various kinds of curves.
In addition, the terminal voltage of the battery does not follow with a sudden change of charge and discharge current, and it takes several minutes to several ten minutes until the terminal voltage is finally settled down to the terminal voltage corresponding to the charge and discharge .current. In other words when the supply of power is stopped, for example, and discharge current becomes 0 [A], relatively long time is necessary for the terminal voltage to be a value of no-load status corresponding to 0 [A] of discharge current.
Therefore, when the residual amount of battery power is detected with voltage method, there is a problem to fall detection precision of residual amount of battery power when residual amount of battery power is detected by such transient time of the terminal voltage.
A change of such terminal voltage of the battery is based on polarization reaction or something like that occurred in inside of the battery. The time interval for the terminal voltage to be constant upon changing charge and discharge cur rent varies depending on charging and discharging current up to that time and also depending on temperature.
FIG. 7 is a characteristic curve showing change of the terminal voltage. The change of the terminal voltage after stopping the power supply with the same discharge current at the time point t1 is shown. As shown by a curve A, it takes long time for the terminal voltage to be constant when the power is supplied for long hours. On the other hand when a power is supplied to the battery for short hours, it takes short time for the terminal voltage to be constant as shown by a curve C in FIG. 7. A change of terminal voltage shown by a curve B is the case where a power is supplied to the battery for an intermediate time.
In order to overcome above defects, a residual charge amount detected by the current integration method is compensated by a residual charge amount detected by the voltage method according to the present invention.
Namely, in accordance with the present invention, a battery control apparatus comprises charge detecting means for detecting change of charge of a battery based on current of the battery, first residual charge amount detecting means coupled to the charge detecting means for detecting a first residual charge amount of the battery by compensating a predetermined reference residual charge amount based on the detected result of the change of charge of the battery, second residual charge amount detecting means for detecting a second residual charge amount of the battery based on a terminal voltage of the battery, and reference residual charge amount updating means for updating the reference residual charge amount by detected result of the second residual charge amount of the battery, wherein the second residual charge amount of the battery is detected at a predetermined timing where the current of the battery is zero or almost zero.
In the battery control apparatus of the present invention, the battery control apparatus is connected to an external device as to form a path for the current between the external device, and the reference residual charge amount updating means generates the predetermined timing by designating the interruption of the current of the battery to the external device.
In the battery control apparatus of this invention, wherein the battery control apparatus includes the battery, and the battery control apparatus is powered by the battery.
Further in the battery control apparatus of this invention, wherein the battery is detachably mounted on the battery control apparatus, and the battery control apparatus is powered by the battery.
In the battery control apparatus of this invention, wherein the current of the battery is charging current of the battery or discharging current of the battery.
This invention further relates to a management method for a battery, comprising the steps of detecting an intermediate residual charge amount of a battery based on a terminal voltage of the battery during the time when current of the battery is almost zero, and detecting a final residual charge amount of the battery based on current of the battery by setting the intermediate residual amount of the battery as a reference.
Further in a management method for a battery of this invention, wherein a predetermined time is set to a time interval where the time that current of the battery is almost zero elapses, and the predetermined time is an interval where changes of the terminal voltage of the battery become stable.